The present invention relates to a method of regulating the drive of a drawing machine or device, respectively, and to a device for drawing metal billets.
Drawing machines or devices, respectively, for drawing billets comprise a plurality of draw plates over which the billet, for instance the wire, is guided in at least one, preferably several coils and is, for the sake of reducing its cross-section, pulled through drawing dies positioned between the draw plates.
Due to the defined cross-section at the entrance of the drawing die and the defined cross-section at the exit of the drawing die, a defined extension of the wire results. In correspondence with the extension of the wire per drawing stage, the speed of rotation of the draw plates per drawing stage also has to be increased.
Due to technologically predetermined wire extensions, correspondingly designed drive gears are used, with which the corresponding differences in the speed of rotation between the individual draw plates are generated by corresponding gear ratios.
Depending on the capability of deformation of the wire material, various drawing sequences were introduced for the drawing dies in drawing technology. The wire extensions resulting from the drawing sequence have to be taken into account in the drawing machine by adapted gear ratios for the draw plates. In order to compensate for deviations in the drawing die sequence or for possible wear of drawing dies, drawing machines having a mechanical gear will operate with slip, i.e. except for the draw-off plate after the last drawing die, all draw plates will rotate too quickly relative to the wire.
This drawing method operating with slip is acceptable only with quite a few wire materials and in wet drawing only. Other materials, such as e.g. steel wire, are drawn without slip in the dry drawing method. Here, the draw plates would immediately wear out in the case of slip, and the wire would be damaged. According to the state of the art, the slip-free operation of these machines is performed by individually driven draw plates with one regulating member each, such as dancer or jockey roller, between the draw plates, or with a wire collection on the draw plates.
In order to improve the operation of a drawing machine operating in such a slide-free way, a method is suggested by EP 679 452 A1 wherein the adjusting and production operation of a multiple drawing machine is to be performed automatically, and wherein the magnitudes or signals, respectively, which are necessary for the regulating process, such as speed of the material and force, each are to be taken over by the drives from the magnitudes of speed of rotation and torque or speed of rotation and current or speed of rotation and performance, and are to be directly measured by measuring devices.
It is not the drive which is positioned last in the direction of material flow that is operated as so-called leading drive, but a speed regulating element is positioned in front of this drive which, in turn, sets a unit load nominal value at its exit which acts as load nominal value for all control and regulating devices.
This method is a very complicated one and is suited exclusively for slip-free drawing processes, i.e. only for steel wires in dry drawing.
Moreover, brakes are provided for at the drives of the draw plates of the slip-free wire drawing machines in order to avoid reversing of the draw plates after the drawing machine has been switched off.